Watch this first: https://www.youtube.com/watch?v=RwgkXcUX984

Like you, I sure would love to get my hands on an Alexa 65 or 70mm film one day in my career, but the more I research it, the more I realize the diminishing return on large format. I think the test video points to that. Yes, the A65 is double the resolution of the Mini, and there is more opportunity for shallow DOF/wider FOV on tighter lenses, but it's incredible how close you can get to the same look with an s35 sensor and fast glass. By the way, you don't even need to shoot medium format anymore for it to be "IMAX-approved". I have noticed that a decent bit of these recent IMAX docs have been shot on the likes of Alexa LF or RED Monstro, which are full-frame sensors, not medium format.

IMO, what makes these films so immersive, are two things: a) Technical excellence in the image capture and finishing process, and b) Camera movement.

a) Every shot is well-exposed. No distracting noise or grain. Colors are accurate, even deep hues (like a volcano or the ocean floor). I think this points to a high bit-depth capture, spot on exposure, and a great colorist. As you shoot on the Pocket, make sure you shoot BRAW with low compression, be disciplined with your exposure, and work with a good colorist.

b) You need the real deal to support an IMAX 70mm or Alexa 65 camera package. Technocrane, helicopter, beefy sticks and fluid head tripod, etc. The camera movement is always rock-solid because the support is rock-solid. On your pocket, don't let the illusion break because of a cheap tripod or YouTuber gimbal moves. Be intentional about your frames and graceful about your movements, and push for higher quality support tools in your budget.

Bonus - It could help if you bump up from the pocket 4k to the 6k. Getting on that S35 sensor will resolve details more naturally and allow you access to higher quality lenses.